This is not entirely true. I don't have much details but I know people who started to work on two separate free software projects aiming to make supported mobile OS. These projects couldn't get funding before but they do now. Afaik it's still a battle with AI companies lobbying that soverign AI is much more important than mobile OS but there is some growing interest. Imho i don't even think some linux based alternative to Android would be that hard to pull off but it's the hw companies that will be skeptical to build hw for such OS. I would have to be some govs puahing it as secure gov devices first.